Surgical graft/stent system

ABSTRACT

A tubular graft/stent includes a tubular sheath ( 10 ) having at intervals along its length a plurality of ring-like rigid members ( 11 ), which are attached to the sheath around their respective circumferences and are made of a shape memory material, so that when the members ( 11 ) change shape the sheath ( 10 ) adopts a new cross section in conformity with them along its whole length. The members may be discontinuous to allow the adoption of a contracted shape in the martensitic phase and an expanded shape in the austenitic phase. A graft may also have a side tube ( 14 ) which can be inverted so as to be housed within the sheath.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International (PCT) PatentApplication Patent Application PCT/GB96/02212 filed 6 Sep. 1996.

BACKGROUND Field of the Invention

This invention relates to a graft/stent system for use in human oranimal surgery. One example of this type of graft/stent is disclosed inEP 0326426A, which describes an artificial blood vessel in the form of atubular sheath having a ring-like member located at each of its ends.Another example, disclosed in EP 0461791A, is an aortic graft with oneof its tubular ends divided into two branches.

SUMMARY

According to an aspect of the present invention, there is provided atubular graft/stent as specified in claim 1.

According to another aspect of the present invention, there is provideda tubular graft/stent as specified in claim 9.

The invention proposes a medical tubular graft stent which comprises atubular sheath having at intervals along its length a plurality ofring-like members, wherein said members are attached to the sheatharound their respective circumferences and are made of a shape memorymaterial, so that when said members change shape, the sheath adopts anew cross-section in conformity with them along its whole length.

Preferably, this provides a compliant tubular sheath, into which aseries of open rings are integrated. The rings act as rigidising membersand are capable of being radially compressed by mechanical forces in themartensitic phase so as to reduce the diameter, and of then returning inthe austenitic phase to a memorised, larger diameter by a thermaleffect.

In a further aspect, the invention proposes a tubular graft comprising atubular sheath having a branch tube which is sufficiently flexible to beinverted so as to be housed within the sheath during an insertionoperation in a human or animal body, and to be redeployed as a branchafter said operation. The sheath and/or the branch tube may employannular rigid members of a shape memory material, as explained above. Inall cases, the members are preferably discontinuous, e.g. a ring with abreak so as to facilitate compression and re-expansion.

In order that the invention shall be clearly understood, severalexemplary embodiments thereof will now be described with references tothe accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a first form of graft,

FIG. 2 shows its compressed form in the martensitic phase in transversecross-section;

FIG. 3 shows its expanded form in the austentitic phase;

FIG. 4 shows an embodiment having a branch tube in its invertedposition;

FIG. 5 shows the FIG. 4 version with the branch tube deployed;

FIG. 6 shows a further embodiment of the present invention; and

FIGS. 7 and 8 show enlarged and developed views of two versions of anoverlap region.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exemplary general arrangement is shown in FIG. 1. A compliant tube 10can be constructed of any flexible material such as cloth, polymers,elastomers or gels. Secured within the compliant tube are a plurality ofexpandable or contractible open rings 11 composed of shape memory alloymaterial. The shape memory alloy rings give structural support to thecompliant tubular sheath and are oriented transverse to the axis of thetube. The cube is circumferentially closed by the overlap 20, but hasfree edges 21, 22. Alternatively, the edges 21, 22 might but oneanother, but this does not provide as much certainty that the tube wallis closed.

The compliant tube 10 can be generated by fabrication methods, or an“open” tube could be made by using flat sheets whose shape isestablished by the shape memory alloy rings. The tubular form might alsouse sheets of dissimilar materials. The cube may be produced incontinuous lengths and cut off as needed.

The shape memory alloy rings can be retained by casting a suitablecompliant material around the ring, by adhesive bonding, sewing or bygenerating a series of pockets within which the rings may be held bywelding, sewing, mechanical fixation or adhesive bonding. In theembodiment shown, the rings 11 are in a single piece, but could be intwo or more accurate sections.

FIGS. 2 and 3 show the compressed (e.g. spiral or rolled-up) andexpanded forms of the tube. The tubular graft/stent is radiallycompressed down to 5.5 mm outside diameter before the device is fittedinto the human body via a delivery catheter. In its expanded form, theoutside diameter might be up to 4 cm.

The device described is suitable for a number of minimally invasivesurgical techniques or may substantially reduce trauma associated withthe introduction of implanted medical devices within a living organism.A single, plain tube (known as a tubular graft) with integratedexpandable contractible rings (known as stents) as described is insertedinto a occluded fluid carrying vessel or a vessel that has a structure.When appropriately positioned via the catheter, heat from the human body(or a heated fluid introduced) will cause the latent geometry of theshape memory alloy to be re-called. Under these circumstances the ringswill expand to a pre-determined position as seen in FIG. 3, the outsidedimensions of which will be slightly larger than the inner dimensions ofthe fluid carrying vessel. Frictional effects will normally retain thegraft/stent in position. However, the shape memory alloy may be arrangedso that when a thermal transition point (memory re-call) is reachedselected sections of the alloy will protrude from the metals surfacepresenting a substantial fixation force. One or more of the alloy ringscould be configured with this additional retention feature.

This device may find applications in surgical repair or maintenanceprocedure for the human body or other animal species. Gastro-intestinalsystem connections, oesophageal cancer, aneurysms, coronary by-passconnections and other vascular by-pass or shunt procedures could employthe stent/graft device.

The dynamic properties of the rings expand the graft/stent within thebody to effect an opening of constricted or occluded vessel. The outergraft stent would assist in preventing occlusive material from onceagain entering the vessel. The complaint sheath will also excludetumorous growth, maintaining luminal patency.

The tubular graft with in integrated shape memory alloy rings may be asimple tube-like form as described or could be a manifold system havinga main tube 13 from which one or substantial numbers of connections 14may be made, as seen in FIGS. 4 and 5. The single a tube or manifoldwill allow fluids to pass in or out of the said connections, to or fromthe main tube structure. The branches extending from the main body canbe of uniform cross-section or of tapering construction.

A graft of the type described might be simply bifurcated or may havenumerous smaller or larger tubes of similar construction, attached tothe main tube body. The branches attached to the body of the device mayhave a similar shape memory alloy ring configuration. Each branch 14 canbe inverted so as to fit within the main tube. Under these conditions,the whole assembly can be radially compressed, the manifold system nowappearing as a single tube for initial insertion via a catheter. Asuitable cord to 15 is connected to the inverted branch enabling it/themto be re-inverted by pulling the cord, as shown in FIG. 5. Preferably,the rings nearer to the main tube are largest and are progressivelysmaller towards the end, to allow the inversion to occur.

When warmed, the shape memory alloy rings will expand to apre-determined position. If employed in a surgical repair, forcesexerted by the shape memory alloy rings will be of sufficient magnitudeto open an occluded vessel thus enabling appropriate fluid flows tocontinue.

The compliant outer sheath would enable radial or axial movement of thevessel to occur. This might be the case if the stent/graft werepositioned in an osophagus that had radially disposed tumours.Peristalsis effects used to assist transportation of food and liquids inthe human body would need to be maintained in oesophageal dysfunctionalproblems. The covered or sheathed stent system would exclude tumorousin-growth and still enable peristalsis to occur.

The compliant could be 0.050 mm polyurethane, polyester or polythene.The shape memory material may be a metal alloy with this property, oralternatively certain mouldable plastics materials such as homopolymersof lactide or glycolide, or copolymers of lactide and glycolide.

The invention is also considered to include a graft with a side tubewhich does not employ stents of shape memory material. Thus in additionto shape memory materials, the ring-like rigid members 11 can also befabricated from elastic materials such as stainless steel or thesuper-elastic forms of nickel-titanium alloys. In this case the implantis constrained within in outer sheath after whose removal the graft willexpand to adopt its final shape.

In the embodiment of FIG. 6, which is of particular benefit in stentingtortuous vessels such as the male urethra, the flexible tubular sheathcan contain slits or openings 23 which are approximately parallel to thering-like members and which allow greater flexion of the implant withoutkinking the sheath. The arrangement of the slits or openings can bevaried with the application and can be positioned to be all on one sideof the cube 23, on alternating sites 24 or spirally arranged along thesheath (25). Other arrangements are possible.

The overlap 20 can be designed to have one of three properties:

1) The overlap can be left to slide freely over itself, permitting thegraft assembly to be contracted by muscles in the vessel or to allowpressure pulses in arterial blood, arising from the heartbeat, to betransmitted to the artery wall. The action of pressure pulses isinvolved in maintaining the vasomotor tone in blood vessels.

The mating surfaces of the overlapping part of the sheath can be coatedto reduce friction and wear with materials such as PTFE or diamond-likecoatings.

2) As shown in FIG. 7, the overlap can incorporate a ratchet-likemechanism which will allow the diameter of the ring-like rigid member toexpand but not to contract. This will guarantee that the lumen of thevessel will be maintained to a minimum diameter and will allow the ringto be locked against the inside of the vessel wall to prevent migrationof the device.

3) As shown in FIG. 8, the overlap can incorporate a ratchet-likemechanism which will allow the diameter of the ring-like rigid membernot to exceed a specified diameter. This is of use where the vessel isfragile and can be exposed to high intraluminal pressures.

The ratchet-like mechanism can be incorporated onto the walls of thesheath by moulding, machining, or attaching ratchet components.Alternatively, the ratchet mechanism can be formed in the ends of thering-like member and can be either permanently present or deployed bythe action of thermal memory.

An implant can be assembled which incorporates a combination of allthree types of overlap mechanism so that for instance, the distal endsof the graft can use ratchet expanding rings to lock the device inplace, while the main body of the graft uses alternating sliding anddiameter-limiting rings to allow limited transmission of pulsatilitywhile restricting the maximum diameter of the graft.

The benefit of the graft can be increased by incorporating coatings ontoits inner or outer surfaces. These coatings can be biomimetics such asphosphorylcholines and proteins, organic biocompatibles such ashydrophilic plastics and inorganic coatings, such as diamond-likecarbon. The coatings can be used to be thrombus-resistant, encrustationresistant or to promote cellular ingrowth. In addition, the coatings canbe used to release locally acting pharmacological agents and they can bemultiply layered.

Deployment of the inverted segment 14 can be achieved by adding a shorthandle, tab or strip to the distal end of the side branch which can beengaged by a snare, forceps or similar engagement means.

1. A tubular graft/stent comprising: a tubular sheath that isgraft/stent; and an integral branch tube having an end fixed to thetubular sheath at an opening in a side wall of the tubular sheath,wherein the branch tube is a graft/stent along its entire length, thebranch tube comprising a plurality of rigid ring-like members being ofprogressively smaller size in the direction progressively away from thetubular sheath, and the branch tube being sufficiently flexible to befully inverted along its entire length so as to be fully housed withinthe tubular sheath during an insertion operation in a human or animalbody, and to be redeployed as a branch after insertion operation.
 2. Atubular graft/stent according to claim 1, wherein the rigid ring-likemembers are made of a shape memory material, so that when said memberschange shape the sheath adopts a new cross-section in conformity withthem along its whole length.
 3. A tubular graft/stent according to claim1, wherein the rigid members are attached to the sheath around theirrespective peripheries.
 4. A tubular graft/stent according to claim 1,wherein said members are discontinuous to allow them to adopt acontracted shape in the martensitic phase, and an expanded shape oflarger circumference in the austenitic phase.
 5. A tubular graft/stentaccording to claim 1, wherein said members can be caused to adopt aspiral form as the contracted shape and a generally circular form as theexpanded shape.
 6. A tubular graft/stent according to claim 1, whereinthe rigid ring-like members are embedded in a compliant material that iscast around said members to form the sheath.
 7. A tubular graft/stentaccording to claim 1, wherein the rigid ring-like members are held inpockets formed in the material of the sheath.
 8. A tubular graft/stentaccording to claim 1, wherein the members are trapped between two layersof material which together form the sheath.
 9. A tubular graft/stentaccording to claim 1, wherein the members include portions which projectfrom the outer surface of the graft in its new cross-section, suchprojecting portions forming anchors for locating the graft in positionin a body.
 10. A tubular graft/stent according to claim 1, wherein thebranch tube has a draw string attached at its free end such that wheninverted into the sheath the draw string may be pulled to redeploy thebranch tube outside the sheath.
 11. A method of inserting a graft/stenthaving a tubular sheath which is a graft/stent and an attached integralbranch tube that is also a graft/stent along its entire length, themethod comprising: fully inverting said branch tube along its entirelength to place said branch tube fully within said tubular sheath forinsertion in a body; inserting said graft/stent into said body; andpulling said branch tube out of said tubular sheath in said body,wherein pulling said tubular branch tube re-inverts said branch tube andleaves said branch tube attached to said tubular sheath.
 12. The methodof claim 11, wherein pulling said branch tube comprises: engaging a cordon a distal end of said branch tube; and pulling said cord to deploysaid branch tube within said body.
 13. The method of claim 12, whereinsaid cord is selected from the group consisting of a draw string, shorthandle, tab, and strip.
 14. The method of claim 11 wherein the sheathincludes at least one ring-like member along its length which is made ofa shape memory material, and wherein the method further comprises thestep of cooling the member.
 15. The method of claim 11 wherein thesheath includes at least one ring-like member along its length, themember having a variable shape wherein it may be at least partiallycoiled, wherein the method further comprises the step of uncoiling themember.
 16. The method of claim 11 wherein the sheath is defined bymaterial which is at least partially coiled, wherein the method furthercomprises the step of uncoiling the sheath from a small-diameter stateto a large-diameter state.